Stuart Kent - Building developer tools at Microsoft - @sjhkent

June, 2005

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    Martin Fowler on Language Workbenches


    Martin has just put up an article on Language Workbenches - IDEs for creating and using DSLs.

    As you'd expect from Martin, this is an insightful piece, with enough follow-on links to keep you interested and busy for days.

    One of the links is to a second article on code generation. Here Martin explains how to write a code generator for a DSL. The first point that comes out is the important distinction between concrete and abstract syntax. This distinction allows a language to have a number of concrete views, which map to the same abstract structure, which code generators then take as input. This saves having to rewrite the code generator every time you add a new concrete view to the language. In our own DSL Tools, we are emphasizing graphical and XML concrete syntaxes for languages. We also generate an API from a language definition which allows direct access to the abstract data structures in memory for purposes such as code generation (all the file handling is done for you).

    Martin continues, in the article, to talk about code generation itself. The first approach he demonstrates is not really a generator at all, but rather an interpreter. This is written in plain code and makes use of reflection. The second approach uses text templates. In generating code for designers from definitions of DSLs, we have found text templates to be our preferred method for writing code generators. We wrote our own text templating engine, which is included as part of DSL Tools. We have taken great care to architect the engine so that it can be integrated into different contexts, which means that it can be hosted in different environements (e.g. inside visual studio or not) and can accept inputs from multiple sources. For DSLs, we've built a Visual Studio host and the extensions that allow direct access within templates to models in memory through the generated APIs mentioned above. My colleague Gareth Jones has blogged about the engine, and there its use in a DSL Tools context is illustrated in the walkthroughs that are part of the DSL Tools download. We're actively working on more complete documentation for the engine itself, including the APIs.

    Aspects that Martin did not touch on in his article include the issues of orchestrating the generation of multiple files from multiple sources, integration with source control (though it is a moot point whether generated files should be checked into source control or not), as well as how to handle cases where 100% code generation is not feasible - particular tricky are the cases where code in the same file has to be further added to - skeleton code is generated, but the programmer has to fill in method bodies, for example. We haven't answers to these yet, but they're on the roadmap.

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    ModeliSoft have updated their Dmd2Dd tool


    For all those who've installed the May 2005 version of DSL Tools (the one that works on VS2005 Beta 2), our friends over at ModeliSoft have just updated their tool - the one that maintains a designer definition as the domain model changes - to work with the new version. The announcement is here. Have fun.

    [Edit - for those of you who can't see the post on the forum, the url is]

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    Transformation workshop at MoDELS 05


    I'm involved in a workshop on model to model transformations at the MoDELS conference this year.

    The call for papers is at

    An interesting feature of this workshop is that they're asking all participants to apply their favourite transformation techniques to a common mapping problem, so the workshop can more easily contrast and compare approaches. The results should be interesting.

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    Back from paternity leave


    Folks probably haven't noticed because of the sporadic nature of my blog entries, but I have been out for two weeks on paternity leave. We now have another daughter called Elsa-Maude. She joins her three sisters and brother.

    I see that whilst I've been out the team put out another release of DSL Tools. I'd flagged this some weeks ago. Jochen has the details. He indicates that we have reworked the text templating engine from previous releases. Unfortunately, we were not able to do it full justice in the documentation. We hope to put that right soon, but in the meantime I see that Gareth has posted more information in his blog.

    Also, TechEd is currently running in the US and our team is represented. Pedro Silva is filing a daily report.

    Meanwhile, time to catch up and get on with the next release...

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    Transcript for DSL Tools web chat


    I see a transcript of the DSL Tools web chat is now available. Members of the DSL Tools team answered questions from customers for an hour or so, and there's some interesting material in there.

    I was hoping to participate in this chat, but Elsa, the latest addition to our family, arrived later than expected. 

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